Channel selection apparatus

ABSTRACT

A channel tuning apparatus which improves operability by eliminating a need for a user to select a CATV mode and allows reliable channel tuning without misjudging the presence or absence of signals even if a frequency of a CATV broadcast is shifted. The channel tuning apparatus includes a tuner ( 2 ) for receiving signals from an antenna ( 1 ), a demodulation unit ( 3 ) for demodulating the received signals coming from the tuner ( 2 ), an input unit ( 6 ) for selecting a specific channel for the tuner ( 2 ), a detection unit ( 4 ) for determining receive mode, and a memory unit ( 5 ) for storing the detected data by the detection unit ( 4 ), in which the channel tuning apparatus is configured to, before performing automatic channel tuning, tune to a specific channel determined by the input unit ( 6 ), detect the receive mode and shift in the received frequency, and store them for use as initial data for automatic channel tuning.

TECHNICAL FIELD

[0001] The present invention relates to a channel tuning apparatus forreceiving digital television signals, especially signals of CATVbroadcasting that has multiple receive modes.

BACKGROUND ART

[0002] Three broadcasting systems are used for CATV broadcasting in theUSA: namely, Standard Cable TV Signals (STD), Harmonic Related Carrier(HRC), and Incremental Related Carrier (IRC) systems.

[0003]FIG. 6 shows picture carrier frequencies (unit: MHz) of theindividual channels (hereinafter “channel” may be abbreviated to “CH”)of the three CATV broadcasting systems. As shown in the figure, all thethree CATV broadcasting systems, STD, HRC, and IRC, have differentbroadcasting frequencies in both CH5 and CH6. For broadcasting on CH5,for example, the STD system uses 79 MHz, HRC system uses 77.75 MHz, andIRC system uses 81 MHz. In this way, the broadcasting frequency varieswith the broadcasting system.

[0004] Since different broadcasting systems use different broadcastingfrequencies as described above, to receive signals of CATV broadcastingthat has multiple receive modes, the channel tuning apparatus likeconventional digital television signal receivers is configured to adoptthe following procedures: when the presence or absence of signals on allchannels are determined automatically, i.e., when automatic channeltuning is performed, a user must determine which broadcasting system isused on each channel for the CATV signals coming into the antennaterminal and then must set the receive mode that corresponds to the typeof broadcasting system, on the channel tuning apparatus, before he/shecan receive CATV broadcasts.

[0005] However, the conventional channel tuning apparatus describedabove has a problem of poor operability associated with the complex andtroublesome manual operations during automatic channel tuning asdescribed above.

[0006] Besides, with a CATV distribution system, in which the CATVbroadcast signals sent from the central station are delivered to homeusers through a number of relay stations, it is necessary to take intoconsideration the fact that the signals may be frequency-shifted alongthe way due to some influence.

[0007] However, when the channel tuning apparatus such as a conventionaldigital television signal receiver is used for tuning, if the frequencyof the desired channel is placed at the center as shown in FIG. 7, thefrequencies within plus/minus 125 KHz from the frequency of the desiredchannel can be pulled in. This range is narrower by orders of magnitudethan the pull-in range for typical analog signals, which is withinplus/minus 1 MHz from the frequency of the desired channel.

[0008] Therefore, if the frequency of the signal delivered by a CATVbroadcast exceeds the pull-in range of the desired channel selected bythe user, there arises another problem that the conventional channeltuning apparatus cannot tune in the delivered signals.

[0009] As described above, the conventional channel tuning apparatus haspoor operability during automatic channel tuning. Also, when selectingan unfamiliar CATV mode, the user may select a wrong mode, resulting inan inability to tune to a channel. Moreover, a proper channel cannot betuned in if the frequency of the CATV broadcast signals is shifted fromthe frequency of the desired channel due to some influence.

[0010] The present invention has been made to solve the conventionalproblems described above. It provides a channel tuning apparatus whichcan improve operability by eliminating the need for a user to select anunfamiliar CATV mode during automatic channel tuning, allow reliablechannel tuning without misjudging the presence or absence of signalseven if the frequency of a CATV broadcast is shifted, and reduce thetime required for automatic channel tuning.

DISCLOSURE OF THE INVENTION

[0011] To solve the above problems, a channel tuning apparatus of thepresent invention is configured to receive signals of CATV broadcastinghaving multiple broadcast modes, and detect and store a CATV broadcastmode and a frequency mode of a channel selected by a user duringautomatic channel tuning out of channels that carry signals or channelnumbers that can be received, whereby each data thus stored is referredto as initial data for automatic channel tuning to tune in and pull indigital signals when the digital signals are received by a tuner.

[0012] This makes it possible to automatically determine a receive modeof a digital CATV broadcast. Then the next time, tuning can be starteddirectly in that broadcast mode. Consequently, the present inventionimproves operability by eliminating a need for a user to select anunfamiliar CATV mode during automatic channel tuning, allows reliablechannel tuning without misjudging the presence or absence of signalseven if the frequency of the CATV broadcast is shifted, reduces the timerequired for automatic channel tuning, and outputs sharp images.

[0013] Going further into the embodiment of the present invention, thechannel tuning apparatus comprises a tuner for tuning to any of channelsthat broadcast digital signals in multiple system modes and receivingthe digital signals; input means for selecting a specific channel forthe tuner to tune to; demodulation means for amplifying, detecting,demodulating, and converting the received signals coming from the tuner;detection means for detecting receive data in the output signals of thedemodulation means to determine the system mode and frequency mode ofthe channel tuned by the tuner; and memory means for storing mode datadetected by the detection means, based on the channel selection by theinput means. The channel tuning apparatus is configured to, beforeperforming automatic channel tuning with respect to the broadcast, makethe tuner tune to the specific channel determined by the input means,make the detection means detect the system mode of the specific channeland the shift in the received frequency on the specific channel, andstore them in the memory means, and the channel tuning apparatus isfurther configured to, when digital signals are received by the tuner inthe automatic channel tuning, use the stored data as initial data forthe automatic channel tuning to tune to and pull in the digital signals.

[0014] According to this configuration, the channel tuning apparatusreceives signals of CATV broadcasting having multiple broadcast modes,and detects and stores the broadcast mode and the frequency mode of thechannel selected by the user during automatic channel tuning out of thechannels that carry signals or the channel numbers that can be received,whereby the stored data is referred to as the initial data for automaticchannel tuning to tune in and pull in digital signals when the digitalsignals are received by a tuner.

[0015] Also, the channel tuning apparatus is configured to, beforeperforming automatic channel tuning, determine whether or not signalsare present on the specific channel selected by the input means. If itis determined that signals are present, the channel tuning apparatussearches an effective range of the received frequency of the receivedsystem mode in sequence and detects and stores any frequency shift foruse as initial data in automatic channel tuning. On the other hand, ifit is determined that no signal is present, the channel tuning apparatusdetects and stores the frequency shift on the first signal-carryingchannel found after starting the automatic channel tuning, and thestored information is used as initial data in the automatic channeltuning.

[0016] According to this configuration, when detecting the CATVbroadcast mode of a user-selected available channel, if the user selectsa channel that carries no signal or if the user selects a wrong channel,the channel tuning apparatus starts automatic channel tuning with thereference CATV mode set to STD mode and the frequency mode set to Centermode as initial data, detects and stores the receive mode and frequencyshift of the CATV broadcast with respect to the first signal-carryingchannel detected after starting the automatic channel tuning, and refersto the stored data as the initial data for automatic channel tuning totune in and pull in digital signals when the digital signals arereceived by a tuner.

[0017] Also, before performing automatic channel tuning, the channeltuning apparatus sequentially searches the effective range of thereceived frequency for the system mode of the channel detected by thedetection means by adding some margin to the range, detects and storesthe frequency shift of each retrieved signal with respect to the centerfrequency, and uses the stored information as initial data in theautomatic channel tuning.

[0018] Thus, the-channel tuning apparatus is configured to detect andstore channels beginning with the channel selected by the user out ofavailable channels or the first signal-carrying channel found afterstarting automatic channel tuning, start channel tuning beginning withthe Center frequency mode, determine the reference frequency mode bysearching a certain effective range in sequence, and perform automaticchannel tuning with reference to the reference frequency mode, therebyallowing channel tuning even if the frequency is shifted due to someinfluence.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram showing a configuration of a channeltuning apparatus according to an embodiment of the present invention;

[0020]FIG. 2 is a flowchart showing an operation of CATV mode selectionaccording to the embodiment;

[0021]FIG. 3 is a flowchart showing an operation of automatic channeltuning according to the embodiment;

[0022]FIG. 4 is a diagram illustrating reference mode search patternsaccording to the embodiment;

[0023]FIG. 5 is a diagram illustrating information about presence orabsence of signals on individual channels;

[0024]FIG. 6 is a diagram illustrating picture carrier frequencies forchannels of CATV broadcasting systems; and

[0025]FIG. 7 is a diagram illustrating a channel tuning method of aconventional channel tuning apparatus.

DESCRIPTION OF THE EMBODIMENT

[0026]FIG. 1 is a block diagram showing a configuration of a channeltuning apparatus according to an embodiment of the present invention.FIG. 2 is a flowchart showing an operation of CATV mode selection. FIG.3 is a flowchart showing an operation of automatic channel tuning. FIG.4 is a diagram illustrating reference mode search patterns. FIG. 5 is adiagram illustrating information about presence or absence of signals onindividual channels.

[0027] Now, the operation performed after a user selects a CATV modewill be described. Regarding CATV broadcast signals supplied to anantenna, each channel can only be in one broadcast mode out of the STD,HRC, and IRC modes at a time, and different modes never coexist on thesame channel. The operation of searching all the channels regardless ofthe presence or absence of signals and storing signal-carrying channelsis referred to as automatic channel tuning.

[0028] Before performing automatic channel tuning, it is necessary toset an appropriate CATV broadcast mode (STD, HRC, and/or IRC mode) aswell as appropriate initial data (also called a reference mode) out ofthe three frequency modes (Center, Minus, and Plus modes), whichrepresent the shift between the frequency of the signals actuallydelivered and the frequency of the desired channel.

[0029] In the block diagram shown in FIG. 1, the modes are set asfollows: before automatic channel tuning, the CATV mode is set to STDmode and the frequency mode is initialized to Center mode and the useris asked to enter, through input means 6, the number of a channel thatcan be received, i.e., a channel that carries signals.

[0030] Next, the channel tuning apparatus calculates the frequency onthe desired channel, i.e., the channel that corresponds to the enteredchannel number, from the current CATV mode and frequency mode, makes atuner 2 tune in and receive the digital signals of the calculatedfrequency through an antenna terminal 1, and makes demodulation means 3amplify, detect and demodulate the digital signals into signals that canbe detected by detection means 4.

[0031] Then, the channel tuning apparatus makes the detection means 4check, with reference to the signals converted by the demodulation means3, whether the channel carries signals. If it is determined that thechannel carries signals, the channel tuning apparatus establishes thecurrent CATV mode as the reference CATV mode, and the current frequencymode as the reference frequency mode. If it is determined that thechannel does not carry signals, the channel tuning apparatus searchesfor signals by changing the CATV mode and frequency mode in sequenceaccording to the search patterns in FIG. 4. Then it repeats the processbeginning with receiving a channel number entered by the input means 6.

[0032] If the channel tuning apparatus cannot determine, after tryingall the search patterns, that the channel carries signals, it sets thereference CATV mode to STD mode and the reference frequency mode toCenter mode. Then it makes memory means 5 store the reference CATV modeand reference frequency mode set by the detection means 4.

[0033] If the reference modes are acquired in this way before automaticchannel tuning, all the channels can be tuned to in sequence accordingto the reference modes and be checked for signals in actual automaticchannel tuning. This eliminates the need to change the CATV mode andfrequency mode for each channel and thus reduces the time required forautomatic channel tuning.

[0034] Now the above operation will be described in detail withreference to the flowchart of FIG. 2.

[0035] Steps S21 to S25, Step S26, and Step 29 represent the searchprocess for reference modes before automatic channel tuning. In otherwords, they represent the process for acquiring a reference CATV modeand reference frequency mode before performing automatic channel tuning.

[0036] In Steps S21 and S22, the channel tuning apparatus makes thetuner tune to the user-selected available channel according to theinitialized CATV mode and frequency mode of that channel. In Step S23,the channel tuning apparatus checks the tuned channel for signals.

[0037] If the channel tuning apparatus determines in Step S23 thatsignals exist on the channel selected by the user, it goes to Step S26,where it stores the current CATV mode and frequency mode as thereference CATV mode and reference frequency mode.

[0038] If the channel tuning apparatus determines in Step S23 that nosignal exists on the channel selected by the user, it goes to step S24,where it checks whether attempts to tune to the channel were made in allthe CATV modes (STD, HRC, and IRC) and whether the frequency-modesearches were made in the effective range (Center, Plus, and Minus),i.e., whether all the search patterns in FIG. 4 were tried.

[0039] If the channel tuning apparatus determines in Step S24 that allthe search patterns shown in FIG. 4 were tried before failing to findany signal on the channel, it goes to Step S29, where it sets thereference CATV mode to STD mode, and the reference frequency mode toCenter mode, to establish these modes as temporary reference values.Then it moves to the next step.

[0040] If the channel tuning apparatus determines in Step S24 that notall the search patterns were tried, it goes to Step S25, where itrepeats Steps S22 to S25 by changing both CATV mode and frequency modeaccording to the search patterns in FIG. 4 until all the patterns aretried.

[0041] The basic search patterns used for the process of Step S25 areshown in FIG. 4. As shown in FIG. 4A, three CATV modes, STD mode, HRCmode, and IRC mode, are available for CATV broadcasting. Besides, asshown in FIG. 4B, three frequency modes, Center mode, Minus mode, andPlus mode, are available to determine the shift in the frequency of thedesired channel.

[0042] Search operations are performed in the following order. First, asearch operation is performed with the CATV mode set to STD mode and thefrequency mode set to Center mode. Next, a search operation is performedwith the CATV mode as it is and the frequency mode switched to Minusmode. Next, a search operation is performed with the CATV mode as it isand the frequency mode switched to Plus mode. Then, a search operationis performed with the CATV mode set to HRC mode and the frequency modeset to Center mode. Subsequently, search operations are performed bychanging the CATV mode and frequency mode in sequence as shown in FIG.4.

[0043] After the reference modes are stored in Steps S26 and S29, thechannel tuning apparatus performs automatic channel tuning in Step S27according to the reference modes stored in the previous step.

[0044] Now the automatic channel tuning operation performed in Step S27will be described in detail with reference to FIG. 3. As shown in thefigure, the channel tuning apparatus starts channel tuning in Step S31according to the stored reference CATV mode and reference frequencymode. In the case of a CATV broadcast, the channels to be tuned are CH1to CH125 as shown in FIG. 6.

[0045] Next, the channel tuning apparatus determines in Step S32 whetheror not signals are present on the channel tuned according to thereference CATV mode and reference frequency mode. If no signal ispresent, the channel tuning apparatus goes to Step S33, where itdetermines whether or not current CATV and frequency modes wereestablished before automatic channel tuning. In other words, the channeltuning apparatus determines whether or not the reference modes wereestablished after signals were found in the user-selected channel or thereference CATV mode and reference frequency mode were set temporarily toSTD mode and Center mode when no signal was found after trying all thesearch patterns.

[0046] If the channel tuning apparatus determines in Step 533 thatreference modes have been established, it goes to Step S35, where itstores information on absence of signals. An example of information onthe presence or absence of signals is shown in FIG. 5. If the channeltuning apparatus determines in Step S33 that no reference mode has beenestablished, that is, if temporary reference modes are used, the channeltuning apparatus determines in Step 534 whether or not all the patternsdescribed above have been tried in order to establish the reference CATVmode and reference frequency mode, that is, whether or not searches wereperformed in the CATV modes (STD mode, HRC mode, and IRC mode) and thefrequency modes (Center mode, Minus mode, and Plus mode) according tothe search patterns in FIG. 4.

[0047] If it is found in Step S34 that searches have been performedusing all the patterns, the channel tuning apparatus goes to Step S35,where it determines that there is no signal on the channel currentlytuned to, and stores information on the absence of signals. If it isfound in Step S34 that not all the patterns were used for searches, thechannel tuning apparatus changes the modes according to the searchpatterns in FIG. 4 and repeats the process beginning with Step S31.

[0048] Now description will be given about the case in which signals aredetected on the desired channel tuned to in Step S32.

[0049] If signals are present, the channel tuning apparatus checks inStep S36, as is the case with Step S33, whether current reference modeshave been established. If they have been, the channel tuning apparatusgoes to step S37, where it stores information on the presence of signalsin memory. If it is determined in Step S36 that no current mode has beenestablished, the channel tuning apparatus goes to step S38, where itestablishes the CATV mode and frequency mode which are currently beingtuned as the reference CATV mode and reference frequency mode, andstores them together with the information on the presence of signals.This means that reference modes are established. Then in Step S37, thechannel tuning apparatus stores the information on the presence ofsignals in memory.

[0050] Next, the channel tuning apparatus makes preparations for thetuning of the next channel in Step S39 and determines in Step S40whether all the channels (CH1 to CH125) have been tuned. If not all thechannels have been tuned, the channel tuning apparatus repeats theprocess starting with Step S31. If all the channels have been tuned, theinformation on the presence or absence of signals for all the channels,which was obtained in Step S27, is stored in Step S28 shown in FIG. 2.

[0051] In this way, if CATV modes and frequency shifts are acquired andstored as established reference modes before automatic channel tuning,the time required for automatic channel tuning can be reducedsignificantly.

[0052] Regarding the problem of narrow pull-in range during the tuningof digital signals, it can be dealt with by establishing a certaineffective range (Center mode, Minus mode, or Plus mode) as a referencefrequency mode which represents the shift from the frequency of thedesired channel. In this way, it is possible to tune to the desiredchannel and output sharp images even if the frequency of the CATVbroadcast signals supplied to the antenna terminal is shifted from thefrequency of the desired channel.

[0053] Although automatic channel tuning of digital CATV broadcastinghas been described above as an example, the present invention cansimilarly be applied to normal tuning, that is, manual channel tuning.

1. A channel tuning apparatus, comprising: a tuner for tuning to any ofchannels that broadcast digital signals in multiple system modes andreceiving the digital signals; input means for selecting a specificchannel for said tuner to tune to; demodulation means for amplifying,detecting, demodulating, and converting the received signals coming fromsaid tuner; detection means for detecting receive data in the outputsignals of said demodulation means to determine the system mode andfrequency mode of the channel tuned by said tuner; and memory means forstoring mode data detected by said detection means, based on the channelselection by said input means, wherein the channel tuning apparatus isconfigured to, before performing automatic channel tuning with respectto said broadcast, make said tuner tune to said specific channeldetermined by said input means, make said detection means detect thesystem mode of said specific channel and a shift in the receivedfrequency on said specific channel, and store them in said memory means,and the channel tuning apparatus is configured to, when digital signalsare received by said tuner in said automatic channel tuning, use thestored data as initial data for said automatic channel tuning to tune toand pull in said digital signals.
 2. The channel tuning apparatusaccording to claim 1, wherein: before performing the automatic channeltuning, it is determined whether or not signals are present on thespecific channel selected by the input means; and if it is determinedthat signals are present, an effective range of the received frequencyof the received system mode is searched in sequence, and any frequencyshift is detected and stored for use as initial data in said automaticchannel tuning; and if it is determined that no signal is present, afrequency shift on a first signal-carrying channel found after startingsaid automatic channel tuning is detected and stored for use as initialdata in said automatic channel tuning.
 3. The channel tuning apparatusaccording to claim 1, wherein said channel tuning apparatus isconfigured to, before performing automatic channel tuning, sequentiallysearch an effective range of the received frequency for the system modeof the channel detected by the detection means by adding some margin tothe range, detect and store the frequency shift of each retrieved signalwith respect to a center frequency, and use the stored information asinitial data in said automatic channel tuning.